Air traffic control uses a complex regime of systems, methods, rules, and procedures, some dictated by government agencies, to ensure safe and efficient movement of aircraft, on the ground and in the air. One aspect of this regime involves evaluation of aircraft-related events at a departure airport to predict events at an arrival airport. For example, whether an airplane makes its arrival slot may depend on whether the same airplane departed on time. Whether an airplane makes its scheduled departure time may depend on events that occur on movement and non-movement areas of the departure (origination) airport.
One example procedure currently in use in this regime is that, after takeoff, aircraft may be directed to merge into en route (Center) airspace traffic flows—the aircraft are “metered.” (In air traffic control, an Area Control Center (ACC), also known as a Center (or in some cases, en-route, as opposed to TRACON control), is a facility responsible for controlling aircraft en route in a particular volume of airspace (a Flight Information Region) at high altitudes between airport approaches and departures. Such a Center also may be referred to as an Air Route Traffic Control Center (ARTCC).) Departure and arrival airports may be in the same Center, or in separate Centers. In some cases, constraints associated with these Center traffic flows create localized demand/capacity imbalances—that is, demand for space or slots in a Center traffic flow exceeds capacity of the Center traffic flow. When demand exceeds capacity, Traffic Management Coordinators (TMCs) at a Center and Frontline Managers (FLMs) at a Local airport may use a procedure referred to as tactical departure scheduling to manage the flow of departures into the constrained Center traffic flow. Tactical departure scheduling usually involves a Call for Release (CFR) procedure in which a Local air traffic control (i.e., at a Local airport Tower) calls the Center to coordinate an aircraft release time prior to allowing the aircraft to depart. Currently, release times are computed at the Center using a Center Traffic Management Advisor (TMA) decision support tool, based upon manual estimates of aircraft ready time that are verbally communicated from the Tower to the Center. The TMA-computed release time then is verbally communicated from the Center back to the Tower where the release time is relayed to the Local air traffic controller as a release window, which typically is three minutes wide. The Local air traffic controller manages aircraft departure to meet the coordinated release time window. Manual ready time prediction by the Local air traffic controller and verbal release time coordination between the Local and Center are labor intensive and prone to inaccuracy. Also, use of release time windows adds uncertainty to the tactical departure process. Currently, many tactically-scheduled aircraft miss their en route slot due to ready time prediction uncertainty.
Furthermore, about 25% of arrival-metered aircraft involve a tactical departure. This means that 25% of inbound flights metered by an arrival TMA system (i.e., at an Arrival Center) are scheduled (i.e., have slots reserved) in the overhead stream while the aircraft still are on the surface at the departure airport. An emerging demand for tactical departure scheduling and the significant uncertainty tactically-scheduled aircraft represent to the en route schedule, increases the importance of integrating departure airport surface information into departure scheduling.
The Aircraft Communications Addressing and Reporting System (ACARS), introduced in 1978, provided a digital datalink system for transmission of short messages between aircraft and ground stations via airband radio or satellite. One aspect of ACARS is the ability to automatically detect and report the start of each major flight phase, called OOOI (gut of the gate, off the ground, gn the ground, and into the gate). About 70% of U.S. commercial flights involve OOOI events. These OOOI events are detected using input from aircraft sensors mounted on doors, parking brakes, and struts. At the start of each flight phase, an ACARS message is transmitted to the ground describing the flight phase, the time at which it occurred, and other related information such as the amount of fuel on board or the flight origin and destination. These messages are used to track the status of aircraft and crews. However, ACARS cannot predict whether an airplane will meet its scheduled states, such as departure states gate pushback, runway entry, and takeoff, and ACARS does not provide information that allows Center and Local flight management personnel to coordinate aircraft departure and thereby improve departure slot performance.
Airport surface surveillance using traditional radar-based or multilateration systems have the potential to improve departure slot performance, but may not be a viable option. Airport surface surveillance systems are very expensive to procure, install, and maintain. The high cost makes these surface surveillance systems impractical for most airports. Furthermore, surveillance in an airport's non-movement presents additional challenges such as limited line-of-sight and multipath interference caused by buildings and other structures. Still further, the FAA is responsible for movement areas of an airport while the airport is responsible for non-movement areas, and the FAA does not surveil the non-movement areas, and does not use non-movement area surveillance. Other complications lessen the reliability of current surface surveillance systems.